Recently, vacuum-based jamming mechanisms have been actively researched for safe human-robot interaction. However, most layer jamming mechanisms provide restricted motion in one direction such that their application in wearable robots is significantly limited. In this article, we propose a novel, soft, multi-degree of freedom (multi-DoF) layer jamming mechanism that employs a sliding linkage-based layer jamming mechanism (SLLJ). SLLJ allows movement not only in linear direction but also in the pitch and yaw directions along with a large resisting force, small thickness, and lightweight compared to conventional layer jamming mechanisms. We designed and fabricated SLLJ components, namely sliding linkage-based layers, soft pins, end holders, and enclosure. In addition, we conducted experimental validation and analysis of its linear tensile resisting force and bending torque in the yaw direction. The proposed SLLJ exhibited maximum resisting force of 264.8 N, compared to 284.1 N of the conventional layer jamming mechanism. Various shapes of SLLJ can be fabricated easily and adapted to a wide range of wearable assistant robots for rehabilitation and injury prevention, which require multi-DoF motions with variable stiffness and substantial resisting force.

A lumbar-degenerative flat back is a condition caused by a decline in back muscle strength with aging. The symptoms of this condition include severe lower back pain and spinal disorders, which restrict people from performing activities of daily living (ADL). Recently, various wearable robots have been developed to assist the weakened muscles. However, despite their effectiveness, the wearables require either bulky and rigid structures (active wearables) or tend to constrain users’ motion (passive wearables). In addition, the complex biomechanics of the human spine have not been sufficiently investigated during the design process. To address these issues, we propose a human-inspired spine assistive robot with a routed twisted string actuator (RTSA, active element) and a flat-back alleviation mechanism (FAM, passive element). This innovative RTSA conforms to the complex human spine curvature while minimizing friction and assists the ADL with its unique prioritizing characteristics. The human spine-inspired FAM, on the other hand, was designed to prevent spinal disorder injury while performing ADL. The experimental results showed that the proposed system successfully reduced the electromyography signals while performing ADL. Furthermore, the spinal disorder injury during trunk motion could be prevented by reducing the lumbopelvic ratio of the users.

Owing to their compliance, lightweight, and high force density characteristics, pneumatic actuation systems have been widely implemented in various soft robots. However, pneumatic actuation systems exhibit low efficiency, poor control performance, and high noise; these make it extremely challenging to widely employ a pneumatic actuation system in mobile robots. To overcome these limitations, many researches were conducted on recycling the compressed air within such systems. However, the proposed approaches do not consider the system efficiency and exhaust performance of pneumatic systems. Therefore, this article proposes a recirculation system using a novel soft re-air valve based on the cardiac structure of fish. In particular, the proposed recirculation system recycles the compressed air to improve the system efficiency and pressurizing performance, and the soft re-air valve simultaneously prevents a decrease in the depressurizing performance. For the validation of the proposed scheme, experiments were conducted to evaluate the system efficiency, control performance, and exhaust noise. In contrast to conventional pneumatic systems, the experimental results revealed that the proposed system increased the overall system efficiency by 47.58%, reduced the position root mean square error by 8.16%, and reduced the exhaust noise by 47.52%.

The twisted string actuator (TSA) has been extensively studied as an alternative to metallic gear reducers due to its low-cost, lightweight, compliance, and highly adjustable actuation characteristics. Owing to these advantages, TSAs were utilized to realize lightweight human-robot interactive robots requiring safe interaction, such as wearables and prosthetics, at a relatively low cost. However, because its force transmission ratio is almost proportional to the length of the string, the string of the conventional TSA must be elongated to achieve high force output. Thus, it is difficult to obtain high force capacity while maintaining a small size. To overcome this limitation, we propose a novel TSA based on parallel bundle-driven actuation to significantly reduce the length of the TSA while achieving high force output. Furthermore, in order to boost the proposed TSA performance, we also present a passive mechanism of an asymmetric behavior compensator. The experimental results show that the force transmission ratio of the proposed TSA is increased by 21%, compared with that of the conventional TSA. Consequently, the proposed TSA has a 44% higher torque capacity with a 37% shorter string than those of the conventional TSA.